Computers include general purpose central processing units (CPUs) or “processors” that are designed to execute a specific set of system instructions. A group of processors that have similar architecture or design specifications may be considered to be members of the same processor family. Examples of current processor families include the Motorola 680X0 processor family, manufactured by Motorola, Inc., the Intel 80X86 processor family, manufactured by Intel Corporation; and the PowerPC processor family, which is manufactured by Motorola, Inc. and used in computers manufactured by Apple Computer, Inc. Although a group of processors may be in the same family because of their similar architecture and design considerations, processors may vary widely within a family according to their clock speed and other performance parameters.
Each family of microprocessors executes instructions that are unique to the processor family. The collective set of instructions that a processor or family of processors can execute is known as the processor's instruction set. As an example, the instruction set used by the Intel 80X86 processor family is incompatible with the instruction set used by the PowerPC processor family. The Intel 80X86 instruction set is based on the Complex Instruction Set Computer (CISC) format. The Motorola PowerPC instruction set is based on the Reduced Instruction Set Computer (RISC) format. CISC processors use a large number of instructions, some of which can perform rather complicated functions, but which require generally many clock cycles to execute. RISC processors use a smaller number of available instructions to perform a simpler set of functions that are executed at a much higher rate.
The uniqueness of the processor family among computer systems also typically results in incompatibility among the other elements of hardware architecture of the computer systems. A computer system manufactured with a processor from the Intel 80X86 processor family will have a hardware architecture that is different from the hardware architecture of a computer system manufactured with a processor from the PowerPC processor family. Because of the uniqueness of the processor instruction set and a computer system's hardware architecture, application software programs are typically written to run on a particular computer system running a particular operating system. Virtual machines can solve any of the problems discussed above that arise from processor and instruction set uniqueness.
It is generally desirable to have more rather than fewer applications run on a microprocessor family. To expand the number of operating systems and application programs that can run on a computer system, a field of technology has developed in which a given computer having one type of CPU, called a host, will include a virtualizer program that allows the host computer to emulate the instructions of an unrelated type of CPU, called a guest. Thus, the host computer will execute an application that will cause one or more host instructions to be called in response to a given guest instruction, and in this way the host computer can both run software designed for its own hardware architecture and software written for computers having an unrelated hardware architecture.
As a more specific example, a computer system manufactured by Apple Computer, for example, may run operating systems and programs written for PC-based computer systems. It might also be possible to use virtualizer programs to execute concurrently on a single CPU multiple incompatible operating systems. In this latter arrangement, although each operating system is incompatible with the other, virtualizer programs can host each of the several operating systems and thereby allow the otherwise incompatible operating systems to run concurrently on the same host computer system.
When a guest computer system is emulated on a host computer system, the guest computer system is said to be a “virtual machine” (or alternatively, it can be referred to as a “partition”) since the guest computer system only exists in the host computer system as a pure software representation of the operation of one specific hardware architecture. The terms “virtualizer,” “emulator,” “direct-executor,” “virtual machine,” “processor emulation,” and virtualization program are sometimes used interchangeably to denote the ability to mimic or emulate the hardware architecture of an entire computer system using one or several approaches known and appreciated by those of skill in the art. Moreover, all uses of the term “emulation” in any form is are intended to convey this broad meaning and is are not intended to distinguish between instruction execution concepts of emulation versus direct-execution of operating system instructions in the virtual machine. Thus, for example, the Virtual PC software created by Connectix Corporation of San Mateo, Calif. “emulates” (by instruction execution emulation and/or direct execution) an entire computer that includes an Intel 80X86 Pentium processor and various motherboard components and cards, and the operation of these components is “emulated” in the virtual machine that is being run on the host machine. A virtualizer program executing on the operating system software and hardware architecture of the host computer, such as a computer system having a PowerPC processor, mimics the operation of the entire guest computer system.
The virtualizer program acts as the interchange between the hardware architecture of the host machine and the instructions transmitted by the software (e.g., operating systems, applications, etc.) running within the emulated environment. This virtualizer program may be a host operating system (HOS), which is an operating system running directly on the physical computer hardware (and which may comprise a hypervisor). Alternately, the emulated environment might also be a virtual machine monitor (VMM) which is a software layer that runs directly above the hardware, perhaps running side-by-side and working in conjunction with the host operating system, and which can virtualize all the resources of the host machine (as well as certain virtual resources) by exposing interfaces that are the same as the hardware the VMM is virtualizing. This virtualization enables the virtualizer (as well as the host computer system itself) to go unnoticed by operating system layers running above it.
In a traditional virtual machine environment, operating systems running in partitions are “unenlightened” in that they are not aware of the hypervisor and believe they are operating on a single physical machine. An operating system that has been modified so that it is aware of the hypervisor is deemed “enlightened” and can use hypervisor services. Moreover, partial enlightenment can be attained by a partition if hypervisor aware code, such as a driver, is installed which uses hypervisor services to redirect requests such as disk, networking, and video operations. It would be advantageous to provide methods and systems related to discovering the hypervisor and then enumerating and utilizing its services for operating system that are enlightened to some degree.